The invention is particularly useful in the atomic absorption spectroscopy; that is, a method for determining the amount of concentration of a looked-for element in a sample. An atomizing device generates an "atom vapor" wherein the components of the sample are present in an atomic state. A measuring light beam from a line-emitting light source, a hollow cathode lamp, for example, is passed through this atom vapor. The spectral lines which are present in the measuring light beam correspond to the resonant lines of a looked-for element the amount or concentration of which shall be determined in the sample. The measuring light beam undergoes an absorption which is determined by the amount or concentration of the looked-for element. Ideally, the measuring light beam is not influenced by the atoms of the other elements which are present in the sample. The fact is used that atoms absorb only such wavelengths from a measuring light beam which they emit with a corresponding excitation in the light source. The attenuation of the measuring light beam in the atom vapor is measured by means of a detector and provides a measure for the looked-for amount or concentration.
It is known to atomize the sample electrothermally. For this purpose, the sample is inserted into a furnace with a furnace body made of graphite. A high electrical current is passed through the furnace body such that the furnace body is heated to a high temperature. Then, a "cloud of atoms" or atomic vapor is generated in the furnace body. The furnace body has a passage through which the measuring light beam is directed such that it passes through the "cloud of atoms".
In a conventional embodiment the furnace body is a graphite tube which is held between two annular contacts. The measuring light beam passes longitudinally through the contacts and the bore of the graphite tube. The sample, mostly present as a solution, is inserted through a lateral aperture into the graphite tube (DE-PS 24 13 781).
The current through and, therefore, the temperature of the graphite tub is modified according to a certain program. At first, the sample is dried at a relatively low temperature, i.e., the solvent is vaporized. Then, in a second step, the remaining sample substance is ashed or decomposed. Finally, the graphite tube is heated to a high atomization temperature, the measurement taking place.
There are furnaces for the electrothermal atomization also known in which current flows through lateral contact elements peripherally around a tubular furnace body (U.S. Pat. No. 4,407,582, DE-0S 35 34 417, Analytical Chemistry 58 (1986), 1973).
It is desired to delay the atomization of the sample relative to the heating of the furnace until there is a constant temperature condition, i.e., the inner wall of the furnace body has achieved its final temperature. Different measures are known by which such a delay is achieved.
It is known to provide in a device for electrothermal atomization of samples a sample carrier separated from the furnace body which projects into a lateral aperture of the furnace body and is heated separately from the furnace body. Then, the furnace body can first be heated to its equilibrium temperature before the heating of the sample carrier is switched on.
Furthermore, it is known to use a sample carrier designed as a small platform in a furnace body designed as a graphite tube. The platform is heated by the heated furnace body substantially indirectly through the radiation emitted by the walls of the furnace body such that the heating of the sample is delayed relative to the heating of the furnace body ("Spectrochimica Acta", 33B (1978), 153-193).
However, the small platform can only accommodate a correspondingly small amount of sample. Therefore, a sample carrier designed as a platform is known which can be inserted into a furnace body designed as a graphite tube, the sample carrier having a recess for accommodating the sample and only being guided into the furnace body along two opposite longitudinal edges (German patent 29 24 123, Company Publication "Variation GTA-96, Graphite Tube Atomizer")
U.S. Pat. No. 3,895,873 describes an atomizing device for electrothermal atomization of samples for atomic absorption spectroscopy in which a furnace body of a square cross-section has a lateral slot in a vertical lateral wall above its lower, horizontal lateral wall. This lateral slot is arranged such that a sample carrier having a recess for accommodating the sample can be inserted into it. When the sample carrier is inserted it comes into close thermal contact to the furnace body. Before the heating up of the furnace body the sample carrier is manually inserted by means of a tool.
British Patent 2,144,871 shows a similar arrangement in which a sample carrier can be inserted into a furnace body designed as a graphite tube through a lateral slot. The sample carrier is inserted before the heating up of the furnace body and is not in heat-conductive contact with the wall of the furnace body.
U.S. Pat. No. 4,202,628 shows a device for electrothermal atomization of samples in which a furnace body designed as a graphite tube has in its center a pot-shaped recess which accommodates the sample. However, this pot-shaped recess is integral with the graphite tube, the heating current constantly flows through both tube and recess. The electrical resistance of the recess is smaller than that of the other graphite tube such that the temperature of the pot-shaped recess is smaller than that of the other graphite tube. Thereby, it shall be achieved that the main portion of the generated atom vapor is in an "absorption cell element" above the recess. This is also true for the stationary condition.
German Patent 23 23 774 shows a furnace body designed as a graphite tube in which the inner wall of the furnace body is provided with slots or a thread. Thereby, the spreading of a sample to the ends of the graphite tube is counteracted.
From German Patent 32 04 873 a device for automatic insertion of a sample into the furnace of an automatic absorption spectrometer is known. In this device a sample carrier is longitudinally inserted into the furnace space of the furnace body by means of a program-controlled gripping device. A plurality of sample carriers is arranged in a movable sample carrier holder and they are consecutively conveyed into the area of the gripping device.